Among all the plants growing in our country, mistletoe is certainly
something special, because its appearance on the trees looks so mysterious.
It grows across the bark and forms huge round shrubby organisms, especially
visible on the foliage trees ; these trees lose their leaves wheras mistletoe
doesn't. It is less visible on spruce-firs and other non-deciduous trees.
It strikes me that plants of mistletoe are distributed widely over some
areas, and are hardly seen in other parts of the country.

Many people have tried to make mistletoe berries germinate on their
trees, but the hardly ever succeeded. Only in rare occasions they were
successful. My own unsuccessful trials made me look for the reason of my
failures and after many years I finally discovered the "Secret of the Mistletoe
Plant". At the same time I found an acceptable explanation why a tree does
not suffer from some mistletoe plants but is destroyed by too many of them.

1.
Distribution.

The seed of mistletoe, arrived on a tree, must try
to survive its long germination process as an epiphyte. It may take a year
before it can such the sap of the tree and become a half-parasite. When
its site is not protected, it is very likely that the seed dries up during
a hot summer or is washed away by a heavy rain-storm.

As for the places where mistletoe can be found, I
should divide these places into three areas, based upon the microclimate
of each area. If this microclimate is favourable for the seed during its
long epiphytic germination process, there will be a favourable evolution.
The requirements are : regular rainfall, a high atmospheric humidity, fog
and nightly condensation during warm and dry spells in the summer so that
the seeds retain enough humidity and do not dry out.

In this kind of microclimate, mistletoe is often
found and we see older, younger and very young plants. All the same too
dry years can occur there, so that seeds dry out ; a germination trial
can fail there. Even there mistletoe cannot be found everywhere sporadically.
In this way the word "microclimate" gets its full meaning.

Next there are areas where mistletoe is not so often
found and young plants are rarely seen. The older and younger plants have
obviously the same age. From time to time there was a favourable microclimate
for the germination.

And then there are certain locations in wich mistletoe
is never found. Even there it sometimes happens, but very exceptionally,
that one or some plants appear, but they will never have descendants. In
this case the favourable microclimate was a very exceptional happening.

Another fact proves that my thesis is right : every
year masses of seeds are spread by birds ; these seeds land on branches
nearly and far away. We may assume that a large part of them will be able
to germinate. The major part however will not succeed in surviving epiphytically
because they simply dehydrate.

It is the germination process which reduces the spreading
of mistletoe in nature and for the same reason the germination is seldorn
successful when we transfer seeds to a host tree.

The reader who does not know the problem should know
that as far as I know, no one ever succeeded in discovering the secret
of the germination process. We see that mistletoe is widely distributed
over some areas and doesn't grow at other places, but so far nobody has
tried to find out why, and they blindly accept the hypothesis "bound to
calcareous areas" without examining whether this thesis is right or wrong.

2.
The Germination Process.

If you break the skin of a berry, you see a liquid,
transparent viscid content and a milky-white little ball of firm pulp in
wich there is one single invisible seed. The whittisch little ball is so
glit that you cannot get the seed out of it. If however you rupture the
skin of the berries and leave them a few days, you will notice that all
the pulp has turned viscid and transparent and now the little seed has
become visible. It is green and it is retained by a net of little fibres.
When it gets dry, the little seed has the colour of wood. Dry it with a
towel and you can watch it : it is flat and oval, but many seeds are much
broader and even heart-shaped.

It is very important to know where you can find the
germ. The fibrous structure leads to one point, the back side which was
connected with the little stem. The germ is always at the opposite side
; it may be recognized by a round spot. The broader seeds always have two
or three germs, which so far nobody seems to have noticed. In order to
germinate, the seed must not necessarily pass trough a thrush's digestive
organs ; it germinates as well when directly placed on a branch.

It is useful to know that, when a trush produces
seeds in a viscid pulp of droppings they eventually land on a branch and
gravitate to wands the underside of the branch or to wands another sheltered
place, especially when the branch is moist.

There the viscid get dry and stick to the branch,
protected from heavy rainfall and the scorching sun, and above all with
a small amount of fertilizer, which might be more usefull than we think
for the absorption of moisture as an epiphyte.

The germination proceeds very slowly : the seed absorbs
water and photosynthesizes because it is green. The germ, green as well,
appears and twins away from the light, towards the branch. As soon as it
touches the branch, its widens and a kind of sucker is formed, wich fixes
itself to the surface of the branch. Now a fine little radicle, is developed
; it goes through the bark and the inner bark, but does not penetrate the
wood. Afterwards - and this may take two years - the "radicle" develops
long cylinder shaped fibres longtwise against the wood. Now new "radicles"
are produced, and they penetrate their hosts' tissues. Only now the seedling
can suck the mineral sap and it becomes independant from the climatological
situation. The little plant is now a half-parasite and will develop its
two first leaves.

As this epiphytic germination may take more than
a year, the possibility of dehydration is very real. Even a favourable
year can have dry spells, so that the seed gets dry. These interruptions
in growth may delay the germination (and be the cause of the long germination
period ?). On the other hand it seems logical that without a lack of moisture
the germination proceeds fluently.

3.
The mistletoe plant.

Mistletoe is dioecious, which means that there are
male and female plants. So far I don't know yet whether one single seed,
showing two or three germs produces only uni sexual or male and female
plants, in that case one simple seed, which has been developed somewhere
completely separately, can still produce berries and seeds.

Mistletoe plants produce a huge amount of nectar,
because the flowers are a meeting-place for bees; this is also proved by
a good fructification; the plants are always loaded with berries. For bee-keepers
it might be very interesting to sow mistletoe on there trees !

Misteltoe grows on practically all kinds of trees
and woody plants, foliage trees as well as conifers. It is never seen on
plane-trees (Platanus) and rarely on beeches (Fagus) and
oaks (Quercus).

The reason is purely technical. The bark of plane-trees
peels off every year and so the seedling is removed before the germination
is finished ; as for beeches and oaks : their bark is covered with a layer
of wax. The glue, wich initially seems to adhere so well, decayes after
some time and so the seedlings are easily removed by the slightest touch.
The adhesion happens only by the intimate contact between the fibres of
the seed and the bark, but when this adhesion is not strong enough, the
seedlings generally fall off. This is the only reason why mistletoe does
not grow on some trees, seldom appears on others and is hardly ever to
be seen on a third kind of trees.

For the druids the oak was a holy tree, and so the
rare mistletoe on oak was very special.

In our country we often see mistletoe on poplar (Populus),
not because it likes to grow on these trees, but because after a long flight,
the mistle thrushes (Turdus viscivorus) tend to rest on these tree-tops
and deposit their faeces there. Consequently these birds involuntarily
locate the situation of mistletoe. So mistletoe does not "choose" the tree,
but it is right that it grows abundantly on some trees wheras the growing
power on other trees is very poor. Mistletoe has a longer, wider or shorter
leaf depending on the kind of host tree. Some people say that there are
different species of mistletoe.

A long time ago the bark of mistletoe was used to
make bird-lime ; people noticed that mistletoe on maple (Acer) and
on elm (Ulmus) produced more bird-lime than other trees. Personally
I think there is a good reason to believe that these are examples of the
so-called "influence of the rootstock" in the cultivation of fruit trees
and ornamental grafted plants. The graft reacts in a different way according
to its rootstock. Obviously for mistletoe there are also physiological
differensces depending on the kind of tree it grows on. Consequently the
definition of "sub-species" does not hold in this case. I am convinced
that, if seed of mistletoe with short leaves is put on a tree, and it forms
long leaves, these seedlings will undoubtedly form long leaves.

Some researchers argue that mistletoe growing on
spruce-fir (Abies), does not germinate on pine (Pinus) and
vice versa. This cannot be true. This assertions is the result of a failing
germination trial. If they had tried a simultaneous sowing test of pine
on pine and spruce-fire on spruce-fire, they would have noticed at once
the failure of the test. As no one so far understood the problem of germination,
no one could sow efficiently.

Some people pretend that mistletoe is an asset to
its host, because it remains green in winter and photosynthesizes, wich
is in favour of the tree. This seems rather unlikely to me because first
of all I do not see how the prepared sap of the mistletoe could penetrate
into the bark of the tree and secondly : if this thesis is true, then trees
covered with mistletoe would grow better, but we can only notice the opposite.
It is also out of the question that the tree is poisoned as some others
pretend, why is one tree, covered with mistletoe, destroyed whereas another
one, with only a few plants, doesn't suffer ? I think I have a logical
answer to this question. The draining of raw sap is only a small loss for
the host tree, but foliage trees lose their leaves and their root system
is asleep during the dormancy. Mistletoe however continues its transpiration
so that a tree, completely covered with mistletoe, is literally drained
; in spring the tree cannot recover anymore ; it has come beyond the "point
of no return".

The phenomenon is identical to the so called "freezing"
of hardy conifers and laurel-cherry (Prunus laurocerasus). This
happens exceptionally when at the same time the soil is frozen and in late
winter a raw east wind together with an already hot sunshine make them
evaporate so rapidly that they get beyond the point of no return. Weeks
later the spruce-firs are completely dehydrated whereas laurel-cherry always
buds.

They are frozen, so we say, but as a matter of fact
they have dried out, their roots not being able to absorb water to compensate
the evaporation.

When mistletoe develops on a thinner branch, we see
that the upper most part disappears and the plant stands at the front end
of that branch. Here too the explanation is quite simple : by quick evaporation
in summer, mistletoe requieres so much raw sap that the upper side of the
branch lacks sufficient supply, dries and perishes ; the dead branch will
be blown off by the next thunder-storm.

A tree covered with mistletoe may get dehydrated
during the summer ; year after year the parasite requires more mineral
sap, so that the viability of the tree decreases progressively.

The tree start to wilt, its photosynthesis is limited,
so that the roots get less nourishment. In the end the tree may even perish,
maybe also after mould infection on its weakened root-system. We also notice
that the mistletoe wilts together with the tree by its lack of mineral
sap.

4. Sowing
Mistletoe.

If you have read the previous lines carefully, you
will understand which points are important if you want your sowing to be
successful. Store the seed at a light, moist place (no refrigerator or
freezer ; they give bad results). When the berries have ripened, you can
sow until late spring. If you start, the skin of the berries should be
ruptured a few days in advance. Smear the seeds over a site at the under
side of a branch, that is averted from the sun. You may make the bark a
bit thinner by cutting out small strips, so that the "radicle" can reach
the bark more easily.

You can also put them into an incision in the bark
but it hardly ever succeeds because the lip which protects the seed so
well, dries up and curls, so that the seed gets lost.

In order to protect the little seed from dehydratation
you can cover it partly with a strip of polyurethanewith
open cells which you fix with a bit of string. Of course the little seed
may stay wet too long so that it perishes afterwards.

We must make a difference between wet and moist.
When something is wet, there is little or no air, whereas moist means that
air and water are both present.

Epiphytes are plants adapted to living in the air
without suffering from lack of moisture. After a rain-shower the surplus
water drains off but the bark (and the air) remain moist for a long time.

Too much water is a problem known only too well both
by amateur and professional orchid growers. The substrate should be of
an open quality and after watering the plants, they may never remain wet
for a long time, only moist.

In our region with the same climate, (the climate
in the middle of West-Europe) mistletoe will grow everywhere if only their
seeds will be placed favourably and provided they will never be wet during
their germination but never be too dry either. This is possible if after
a day without rains, the are sprayed with rain-water, to wich you add 1
cc of leaf-nutriënt as the green little seed and the green germ photosynthesize
to develop. This thesis makes much more sense than pretending that the
little seed has enough reserve to last a whole year, the duration of the
germisation. The photosynthese supply the reserve from the seed.

5.
About thrushes and the dissemination of the seeds.

Because there are quite a lot of misgivings about
the dissemination of seeds by the Turdidae, I want to place this dissemination
in the correct context.

The mistle thrush (Turdus viscivorus) spreads
the seeds over a long distances. In our country, the return flight of the
migrating thrushes takes place in February/March. The birds fly back from
the south, where there is mistletoe, to the north, where there isn't.

It is wrongly believed that distances over 2 km cannot
be bridged and that the seeds have already been excreted after half an
hour. The trush proves otherwise !

When prolonged efforts are produced, most of the
blood streams towards the muscles, and the digestive system almost stops
completely. It is possible that the observation of captive thrushes shows
that the seeds appear after only half an hour, but migrating birds cover
huge distances before resting in high trees where they defecate.

"Mistletoe in the Creek District" is a classic example
of this. I estimate the nearest source population at a distance of 50 km
by air.

Alost brings a similar proof. All mistletoe is found
on the first row of the trees, not in the middle, not at the back, but
at the south side of the poplars wood. So the thrushes came from one direction
and, obviously,they rested on the first row of trees
!

When we find mistletoe on an row of poplars in a
Brussels cemetery, the same explanation is valid.

The allegation that this mistletoe is a local contamination
from the mistletoe branches laid on the graves cannot be substantiated.
The mistle thrush won't eat there and then fly to the poplars. The blackbird
(Turdus merula) and the song-thrushes (Turdus ericetorum philomelos)
can eat these berries, but then they won't fly high up into those big poplars,
they will prefer the lower trees and bushes of their own habitat.

My explanation is logical. Some ten years ago, there
was an exceptionally humid year in Flanders, favorable for germination.
All this mistletoe appeared some years later in the Creek District, Alost,
Hekelgem, Brussels and perhaps other places. So they have all the same
age and this can easily be established !

During that year, many branches of mistletoe were
probably also deposited in many cemeteries, and blackbirds and song thrushes
could have disseminated the seeds locally ... but mistletoe was never reported
in the churchyard trees ! As you see, it's not as simple as it looks.

Further on, I will explain why the seeds that are
deposited onto trees late in the season (when the thrushes migrate back)
have the greatest chance of germinating successfully (provided that the
summer is favorable, and this is very very exceptional in Flanders). We
mustn't forget that the thrushes disseminate the seeds in the same way
year after year, and that, every year, these seeds also dry out during
the summer. The seeds of the berries in the graveyards, on the contrary,
are deposited on the trees during the winter by the local thrush population,
and this is much less favorable.

6.
How does the seedling evolve ?

When the suction pad has attached itself, the green
seedling grows visibly thicker and, at the same time, the seed thins. The
reserves are used to develop the plunger, and photosynthesis has a complementary
action.

The strong germ will then lift the emptied seed,
and this means that the glue is exhausted. Later on, the seed-case drops
off and the only thing remaining is a small green stem, a little stump
of circa 4-5 mm.

In the autumn, there is enough moisture for the seedling
not to dry out, but in winter, frost has a very dehydrating effect. If
the plunger has not reached the sapwood, the seedling will dry out. And
as the seedling does not dry out, this proves that the plunger has already
reached the "source" in autumn. So this meaningless green stump has already
become an independent half-parasite in autumn. This slow germination and
the associated epiphytic live do not last longer than one year, but (only)
from spring to fall. However, it is possible that certain seedlings do
not reach the sapwood before the winter. I think that these will dry out
and die during the winter.

Naked seeds on a branch can also dry out, but not
those that are still inside berries. It is impossible to imagine that they
would die during the winter and that the ones that would germinate later
on would be disseminated by the birds (or people) when the frost season
is over or even later.

When seeds are deposited "normally", the best period
is from December till late spring, but in the winter there's an additional
risk. Birds are hungry and the blue tit (Parus caeruleus) liks these
seeds... In March/April, however, there are already a lot more insects,
and then the birds prefer hunting. This is an additional argument for putting
out the seeds later in spring.

During this long germination process, the temperature
plays an important part.

In early spring, days can be pleasantly warm, but
nights stay cold. That is why plants usually start growing when the nights
get warmer as well.

Mistletoe reacts in the same way. The germination
process starts late and slowly, when the night temperatures rise significantly.

I think that the further development also stops when
nights get cooler in the fall. The consequence appears from the fact that
most seedlings only grow their first two leaves when the winter is over
and when the temperatures are once more favorable for their growth. In
the youth stages of mistletoe (germination and seedling), I see many similarities
with epiphytes. Whitin certain small limits, they resist a lot wait till
the growing circumstances are favorable again. Without these limits, however,
they die quickly.

7.
How to obtain successful seedlings ?

Until now, all the "accesories" that I devised to
help the seeds germinatig were less successful than just gluing the naked
seeds with their own glue onto the branches.

The long germination is a consequence of the slow
development, which is itself influenced by the prolonged cold (nights)
in spring.

In horticulture seeds are already sown out in greenhouses
during the winter in order to make them bloom in April/May. If the mistletoe
seeds are given warmth, moisture and light early on, the seedlings will
develop earlier and in March/April they will then be ready to be glued
on a branch.

This really is the only useful technique.

Method :

Harvest ripe berries around the turn of the year
and place them next to each other onto a sheet of wet kitchen roll in a
dish. Cover the dish with a glass pane and keep moist. Put the dish in
a warm (16 à 18 ° C) and light place out of directly sunlight.
The seeds will then germinate within the berries.

Around mid-February, remove the paper and make the
berries burst. Wait until the pulp has become liquid and translucent.

Carefully take the seeds out and glue them on the
bottom of a dark-colored dish, about 1 cm apart. Let the glue set and moisten
the seeds slightly with a spray. If you moisten them too much, the seeds
will slide to one another.

Also spray the underside of the glass before covering
the dish and putting it once more into a warm and light place.

Repeat daily : first let them dry, then moisten them.

When you have taken all the seeds out of the berries,
try and collect as much liquid, sticky pulp as you can in a small jar that
you keep in the fridge.

First, the shoots develop just straight as they come
out of the seeds. After having reached a certain height, they will turn
towards the dark side, i.e. the bottom of the dish. As soon as the shoot
touches the bottom of the dish, you must put the dish outside on the windowsill
out of the sun, there it is cold and clear, and then glue them onto a dry
branch with the glue you collected from the berries. Possible night frost
won't do any harm.

These geminated seeds will have taken enough head
start to grow their first leaves in the coming fall. There is one absolute
necessity : they must never dry out during the summer.

In my conviction mistletoe will be found in the future
by amateurs everywhere as long as the little seeds will be helped efficiently
during their epiphytic germination process.

Do not be afraid : the area will not be damaged by
extensive colonies of mistletoe. After all the trouble that has been taken,
you will understand that the seeds of your plants, whish will be spread
in a natural way by thrushes, will not have a chance to survive in an area
where the microenvironment is not favourable for the germination, in an
area where generally no mistletoe is being found.

In areas more in the north, mistletoe cannot be found
anymore. In my opinion this is due to the fact that there are a lot of
short warm periods during the summer in that area. As a consequence the
germs have not enough time to reach the sapstream which causes the seeds
to dry out during the winter.

By using the method for pre-germination, it may be
possible to let the mistletoe grow on trees in the north.

An other possibility consists in letting the mistletoe
germinate on trees, in containers placed in a nursery. When the germination
is succesful the trees can be then planted in the areas situated in the
north. When the germination is a success, I am sure that the little trees
will develop anywhere apart from the place where they are planted and,
in my opinion they will even grow in the tree frontier.

This drawing shows the seed at its normal size and
also enlarged to show how the fibres comes together in one point. The germ
is always at the opposite side. Broaden seeds have two or three germs.

When the seed is in the berrie, it is green,but when
the fibres are dry, they are light brown, there is no doubt that this fibres
are hygroscopic.

Photo : Guy LAURENT
This macro-picture of my germination trial was taken
July 12th, 1985. This seed develops two germs and the little sucker is
being formed : the hottest summer spell is still to come and may dry the
little seed. We can also distinguish all sorts of lichen and scales, probably
brought there by the wind and having established themselves. All this helps
to absorb moisture and store it for the seed. Especially for the tangent
place seed/bark the water is stored.

This is the copy of a photograph on the front page
of "Bulletin de la Société Royale Linnéenne et de
Flore" (Octobre/Décembre 1977). It shows us a germinating seed of
mistletoe but here too,nobody noticed that one single seed developed three
germs. Notice the favourable spot where this little seed happened to land.
It has every chance to survive : young wood (thin bark), well protected
from the powing rain ; let's just hope it will not dry up.